Tunable optical devices, such as tunable lasers, have been implemented in a variety of applications such as telecommunications, computer networking, and medical technology. Dense wavelength division multiplexing (DWDM) equipment utilizes tunable laser technology to maximize the available bandwidth of optical fiber networks. In DWDM optical systems, multiple separate data streams propagate concurrently in a single optical fiber, with each data stream created by the modulated output of a laser at a specific channel frequency or wavelength. Presently, channel separations of approximately 0.4 nanometers in wavelength, or about 50 GHz are achievable, which allows up to 128 channels to be carried by a single fiber within the bandwidth range of currently available fibers and fiber amplifiers. Greater bandwidth requirements will likely result in smaller channel separation in the future.
When tuning a tunable laser to a specific wavelength, various methods are used to keep the device on the selected wavelength. Wavelength locking designs are commonly implemented with hardware structures utilizing analog circuitry. However, because of their physical size, such analog hardware wavelength locking designs have limited miniaturization capability. Analog hardware structures are also susceptible to error caused by environmental temperature changes, aging of the hardware equipment, and sensitivity to noise. In addition, analog hardware wavelength locking schemes are not easily synchronized with other control functions of a tunable laser. Lastly, analog hardware wavelength locking schemes are difficult to update in light of changes to laser hardware designs.